Revert "devenv: Set PYTHONPATH where we install python modules"

This reverts commit 79c6075b560dbf1c3e4e0b30f1c472dc2086421e.

# Conflicts:
#	docs/markdown/snippets/devenv.md
#	mesonbuild/modules/python.py
#	test cases/unit/91 devenv/test-devenv.py

PYTHONPATH cannot be reliably determined. The standard use case for
installing python modules with Meson is mixed pure sources (at least
`__init__.py`) and compiled extension_modules or configured files.
Unfortunately that doesn't actually work because python will not load
the same package hierarchy from two different directories, one a source
directory and one a (mandatory) out of tree build directory.

(It kind of can, but you need to do what this test case accidentally
stumbled upon, which is namespace packages. Namespace packages are a
very specific use case and you are NOT SUPPOSED to use them outside that
use case, so people are not going to use them just to circumvent Meson
devenv stuff as that would have negative install-time effects.)

Adding PYTHONPATH anyway will just lead to documentation commitments
which we cannot actually uphold, and confusing issues at time of use
because some imports *will* work... and some will *not*. The end result
will be a half-created tree of modules which just doesn't work together
at all, but because it partially works, users attempting to debug it
will spend time wondering why parts of it do import.

For any case where the automatic devenv would work correctly, it will
also work correctly to use `meson.add_devenv()` a single time, which is
very easy to manually get correct and doesn't provide any significant
value to automate.

In the long run, an uninstalled python package environment will require
"editable installs" support.

1 files changed, 6 insertions, 43 deletions

diff --git a/mesonbuild/modules/python.py b/mesonbuild/modules/python.py
index 3eac33f..70ae3c1 100644
--- a/mesonbuild/modules/python.py
+++ b/mesonbuild/modules/python.py
@@ -23,7 +23,7 @@ from . import ExtensionModule
 from .. import mesonlib
 from .. import mlog
 from ..coredata import UserFeatureOption
-from ..build import known_shmod_kwargs, EnvironmentVariables
+from ..build import known_shmod_kwargs
 from ..dependencies import DependencyMethods, PkgConfigDependency, NotFoundDependency, SystemDependency, ExtraFrameworkDependency
 from ..dependencies.base import process_method_kw
 from ..environment import detect_cpu_family
@@ -48,7 +48,6 @@ if T.TYPE_CHECKING:
     from ..interpreter import Interpreter
     from ..interpreter.kwargs import ExtractRequired
     from ..interpreterbase.interpreterbase import TYPE_var, TYPE_kwargs
-    from ..backends import InstallData
 
     class PythonIntrospectionDict(TypedDict):
 
@@ -400,20 +399,6 @@ class PythonExternalProgram(ExternalProgram):
             'variables': {},
             'version': '0.0',
         }
-        self.devenv_pythonpath: T.Set[str] = set()
-
-    def add_devenv_pythonpath(self, basedir: str, subdir: str, install_subdir: str) -> None:
-        # If we install python module into 'foo/bar' subdir, we need the last 2
-        # parts of source dir to be ['foo', 'bar'] and set PYTHONPATH
-        # pointing grandparent directory. That way scripts will be able to
-        # `import foo.bar.something` just like when the are installed.
-        # If the source tree layout does not match installed layout there is
-        # nothing we can do.
-        install_subdir_parts = Path(install_subdir).parts
-        subdir_parts = Path(subdir).parts
-        if subdir_parts[-len(install_subdir_parts):] == install_subdir_parts:
-            pypath = os.path.join(basedir, *subdir_parts[:-len(install_subdir_parts)])
-            self.devenv_pythonpath.add(pypath)
 
     def _check_version(self, version: str) -> bool:
         if self.name == 'python2':
@@ -522,10 +507,8 @@ class PythonInstallation(ExternalProgramHolder):
             subdir = kwargs.pop('subdir', '')
             if not isinstance(subdir, str):
                 raise InvalidArguments('"subdir" argument must be a string.')
+
             kwargs['install_dir'] = os.path.join(self.platlib_install_path, subdir)
-            self.held_object.add_devenv_pythonpath(
-                self.interpreter.environment.get_build_dir(),
-                self.interpreter.subdir, subdir)
 
         # On macOS and some Linux distros (Debian) distutils doesn't link
         # extensions against libpython. We call into distutils and mirror its
@@ -580,19 +563,11 @@ class PythonInstallation(ExternalProgramHolder):
     def install_sources_method(self, args: T.Tuple[T.List[T.Union[str, mesonlib.File]]],
                                kwargs: 'PyInstallKw') -> 'Data':
         tag = kwargs['install_tag'] or 'runtime'
-        pure = kwargs['pure']
-        sources = self.interpreter.source_strings_to_files(args[0])
-        install_subdir = kwargs['subdir']
-        install_dir = self._get_install_dir_impl(pure, install_subdir)
-        builddir = self.interpreter.environment.get_build_dir()
-        srcdir = self.interpreter.environment.get_source_dir()
-        for src in sources:
-            basedir = builddir if src.is_built else srcdir
-            subdir = os.path.dirname(src.relative_name())
-            self.held_object.add_devenv_pythonpath(basedir, subdir, install_subdir)
-        return self.interpreter.install_data_impl(sources, install_dir,
+        return self.interpreter.install_data_impl(
+            self.interpreter.source_strings_to_files(args[0]),
+            self._get_install_dir_impl(kwargs['pure'], kwargs['subdir']),
             mesonlib.FileMode(), rename=None, tag=tag, install_data_type='python',
-            install_dir_name=self._get_install_dir_name_impl(pure, install_subdir))
+            install_dir_name=self._get_install_dir_name_impl(kwargs['pure'], kwargs['subdir']))
 
     @noPosargs
     @typed_kwargs('python_installation.install_dir', _PURE_KW, _SUBDIR_KW)
@@ -660,18 +635,6 @@ class PythonModule(ExtensionModule):
             'find_installation': self.find_installation,
         })
 
-    def get_devenv(self) -> T.Optional[EnvironmentVariables]:
-        pythonpath = set()
-        for python in self.installations.values():
-            version = python.info['version']
-            if mesonlib.version_compare(version, '>=3.0'):
-                pythonpath |= python.devenv_pythonpath
-        if pythonpath:
-            env = EnvironmentVariables()
-            env.prepend('PYTHONPATH', list(pythonpath))
-            return env
-        return None
-
     # https://www.python.org/dev/peps/pep-0397/
     @staticmethod
     def _get_win_pythonpath(name_or_path: str) -> T.Optional[str]: